The present invention relates to a fuel-air mixture apparatus, particularly for an internal combustion engine.
Fuel-air mixture apparatuses of the type where fuel is mixed with air prior to induction into the cylinder(s) of an engine generally rely on a pressure reduction at a throttle in the device to draw fuel into the device, in which case the device is known as a carburettor, or rely on fuel injection into the air as it passes through the device.
Generally, the prior devices rely on a single stage of mixture of fuel and air and are limited as regards the droplet size and total vaporisation of the fuel in the air which they induce. Inadequate vaporisation and too large a droplet size result in unburned and/or incompletely burnt fuel being present in the exhaust from the engine.
In my International Application No WO 97/48897, I have described and claimed an invention which I refer to below as xe2x80x9cMy Earlier Inventionxe2x80x9d and which comprises a fuel-air mixture apparatus having:
a primary air passage having an inlet, an adjustable throttle and an outlet,
a secondary air passage having an inlet and an outlet to the primary air passage between its adjustable throttle and its outlet,
a variable orifice nozzle for introducing fuel into the secondary air passage, the nozzle having a mouth and a down-stream pointing tapered needle in the mouth to provide variability of the orifice by axial movement of the needle and
a linkage or control device for linking or controlling the position of the needle to the position of the adjustable throttle in the primary air passage for adjustment of the orifice of the nozzle,
the arrangement being such that in use the fuel mixes with the air flowing through the secondary air passage prior to mixing with the air flowing in the primary air passage and the fuel flow from the nozzle is matched to the position of the adjustable throttle.
The object of the present invention is to a further improved fuel air mixture apparatus.
The invention is based on passing a fuel-air mixture through an apertured vaporisation block in the apparatus to enhance the degree of mixing of the fuel with the air.
According to my present invention, there is provided a fuel-air mixture device comprising:
a primary air passage having an inlet, an adjustable throttle and an outlet,
a variable orifice nozzle for introducing fuel to the primary air passage, the nozzle having a mouth and a tapered needle in the mouth to provide variability of the orifice by axial movement of the needle, the needle being arranged transversely of the primary air passage and
a linkage or control device for linking or controlling the position of the needle to the position of the adjustable throttle in the primary air passage for adjustment of the orifice of the nozzle and
an apertured vaporisation block having a plurality of air passageways through the block, which subdivide a portion of the primary air passage between the fuel introduction position and the outlet.
The apertured vaporisation block may be integral with a member defining the primary air passage. Alternatively it may be fitted to the latter. In this case, the apertured vaporisation block may be mounted in such manner as to be ultrasonically excitable. Typically this can be by mounting the block in an ultrasonically excitable ring. Alternatively, the passageways in the block can be lined by ultrasonically excitable tubes.
The apertured vaporisation block can be a solid block in which the air passageways are formed by machining or casting. Alternatively, the apertured vaporisation block can be laid up from a plurality of layers, preferably by winding, the layers having regular formations extending out from each layer to space it from the next layer. The formations at each layer can be continuous with the formations at the next or inter-spaced with the formations at the next.
In one preferred embodiment, the apertured vaporisation block is provided wholly downstream of the position of the fuel introduction means, preferably with an upstream face of the apertured vaporisation block being formed concavely, preferably conically.
In another preferred embodiment, the apertured vaporisation block is provided at and extending downstream of the position of the fuel introduction means.
Whilst I envisage the contrary, I prefer that the present fuel-air mixture apparatus should be fully in accordance with My Earlier Invention, that is to say incorporating:
a secondary air passage having an inlet and an outlet to the primary air passage between its adjustable throttle and its outlet,
the arrangement being such that in use the fuel mixes with the air flowing through the secondary air passage prior to mixing with the air flowing in the primary air passage and the fuel flow from the nozzle is matched to the position of the adjustable throttle.
In the embodiment wherein the apertured vaporisation block is provided at and extending downstream of the position of the fuel introduction means, the apertured vaporisation block has at least one transverse bore leading from the secondary air passage to a respective one of the air passageways through the block. Each of the passageways can have a transverse bore leading from the secondary air passage. Alternatively, some of the air passageways may not be in communication with the secondary air passage and not receiving fuel-air mixture in use. Some of the air passageways may be in communication with the secondary air passage only via others of them.
The fuel introduction needle may extend into one or more of the air passageways in the apertured vaporisation block.
It is envisaged that the passageway(s) having the transverse bore(s) can be configured as venturi(s) with the narrowest throat(s) being at the orifice(s) of the transverse bore.
To aid mixture of the fuel with the air in the passageways, the latter can have turbulence inducing formations downstream of the transverse bore.